Your debug log shows Pi-hole to be active and filtering, with full IPv4 connectivity.
With regard to IPv6, you have gateway connectivity, but Pi-hole seems to be using an invalid or expired IPv6 address (click for details)
(excerpt shortened for relevant sections)
*** [ DIAGNOSING ]: Networking
[✓] IPv6 address(es) bound to the eth0 interface:
2601:8c0:xxxx:63f0:394e:cc66:xxxx:xxxx does not match the IP found in /etc/pihole/setupVars.conf
[i] Default IPv6 gateway
[✓] Gateway responded.
*** [ DIAGNOSING ]: Name resolution (IPv6) using a random blocked domain and a known ad-serving domain
[✓] ads.youniversalnext.com is :: via localhost (::1)
[✗] Failed to resolve ads.youniversalnext.com via Pi-hole (2601:8c0:xxxx:63f0:a1b6:9e8:xxxx:xxxx)
[✓] doubleclick.com is 2607:f8b0:400f:805::200e via a remote, public DNS server (2001:4860:4860::8888)
*** [ DIAGNOSING ]: Setup variables
IPV6_ADDRESS=2601:8c0:xxxx:63f0:a1b6:9e8:xxxx:xxxx
For devices preferring IPv6 over IPv4 (often smartphones), this may result in the behaviour you observe (i.e. no filtering and/or failed name resolutions), as such a device may either contact your ISP's IPv6 DNS server or fail.
Likely, your global IPv6 address has changed since you installed Pi-hole (as is common for IPv6 Privacy Extension addresses).
It also seems you are currently not using an IPv6 ULA address (click for more)
While there is indeed much more to IPv6 addresses, the following are relevant for your network configuration:
| range | description | visibility |
|---|---|---|
fe80::/10 |
link-local | private network, same local segment only |
fd00::/8 |
unique local (ULA) | private network, potentially all local segments |
2000::/3 |
global unicast | all networks - public Internet and private network |
As stable address assignment is mandatory for Pi-hole to work, you should consider using a ULA address instead, see Use IPv6 ULA addresses for Pi-hole .
And if your router does not support ULA prefix assignment? (click for more)
You could try and use your Pi-hole machine’s non-routable(!) link-local IPv6 address (from fe80::/10 range).
Note that devices need to be within the same network segment for this to work, i.e. commonly all devices need to connect directly through your router - any L3 switching will prevent devices connected through such a (edit: additional) switch/router/AP to see and communicate with Pi-hole’s link-local address.
Once you assigned a ULA prefix or decided you can use link-local, you can find out about IPv6 addresses associated to your Pi-hole’s eth0 interface with
ip -6 addr show eth0
You’d then have make Pi-hole aware of its new address by running
pihole -r
and choose reconfigure .
Alternatively, you could try and disable IPv6 altogether if your router allows it.